U.S. patent application number 13/041677 was filed with the patent office on 2011-09-15 for optical disc drive and method for reading data from optical disc.
Invention is credited to Takahiro SATO, Takeshi SHIMAMOTO, Hiroshi YOSHIDA, Akihito YOSHIMI.
Application Number | 20110222382 13/041677 |
Document ID | / |
Family ID | 44123311 |
Filed Date | 2011-09-15 |
United States Patent
Application |
20110222382 |
Kind Code |
A1 |
SATO; Takahiro ; et
al. |
September 15, 2011 |
OPTICAL DISC DRIVE AND METHOD FOR READING DATA FROM OPTICAL
DISC
Abstract
An optical disc drive and optical disc reading method according
to the present invention is designed to perform a read operation
with good stability even on a slim disc that could produce a
significant axial runout. For that purpose, the optical disc drive
determines, by the time it has taken for the number of revolutions
of a motor that rotates the optical disc loaded to reach a
predetermined number, whether the disc loaded is a lightweight disc
or not (in Step 202). The drive also determines, by a signal
obtained from the optical disc, what the size of the optical disc
loaded is (in Step 204). And if the drive decides, based on results
of these processing steps, that the disc loaded is a slim disc,
then the drive increases the number of revolutions of the optical
disc to a predetermined number or more in Step 207 to minimize the
influence of axial runout.
Inventors: |
SATO; Takahiro; (Osaka,
JP) ; YOSHIMI; Akihito; (Osaka, JP) ;
SHIMAMOTO; Takeshi; (Osaka, JP) ; YOSHIDA;
Hiroshi; (Osaka, JP) |
Family ID: |
44123311 |
Appl. No.: |
13/041677 |
Filed: |
March 7, 2011 |
Current U.S.
Class: |
369/47.38 ;
369/47.1; G9B/7.005; G9B/7.018 |
Current CPC
Class: |
G11B 19/28 20130101;
G11B 19/12 20130101 |
Class at
Publication: |
369/47.38 ;
369/47.1; G9B/7.018; G9B/7.005 |
International
Class: |
G11B 7/0037 20060101
G11B007/0037; G11B 7/005 20060101 G11B007/005 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2010 |
JP |
2010-055735 |
Claims
1. An optical disc drive with the ability to read data from both a
normal thickness disc, which has a thickness of 1.2 mm and that has
stored data thereon, and a slim disc, which has a thickness of 1.0
mm or less and that has also stored data thereon, the drive
comprising: a motor for rotating a disc loaded; an optical head for
focusing a light beam on the disc that is being rotated by the
motor; and a control section for controlling the operations of the
motor and the optical head, wherein when reading data from the slim
disc, the control section makes the motor or the optical head
operate under a different operating condition than when reading
data from the normal thickness disc.
2. The optical disc drive of claim 1, wherein the operating
condition includes at least one of the number of revolutions of the
motor, the gain of a focus control, and a radial location on the
disc at which the light beam that irradiates the disc needs to be
focused.
3. The optical disc drive of claim 1, wherein the control section
includes a disc type recognition section for determining whether
the disc loaded is a slim disc or not.
4. The optical disc drive of claim 1, wherein if the disc loaded is
the slim disc, the control section raises the lower limit of the
number of revolutions of the motor.
5. The optical disc drive of claim 1, wherein if data cannot be
read properly from the disc loaded by operating the motor and the
optical head under an operating condition for reading the data from
the normal thickness disc, at least a part of that operating
condition is changed into an operating condition for reading data
from the slim disc.
6. A method for reading data from an optical disc loaded by using
an optical disc drive that is compatible with both a normal
thickness disc, which has a thickness of 1.2 mm and that has stored
data thereon, and a slim disc, which has a thickness of 1.0 mm or
less and that has also stored data thereon, the method comprising
the steps of: rotating the optical disc loaded; irradiating the
optical disc with a light beam; and if the optical disc loaded is
the slim disc, making the optical disc drive operate under a
different operating condition from when reading data from the
normal thickness disc.
7. The method of claim 6, comprising a disc type recognizing step
for determining whether the disc loaded is the slim disc or
not.
8. The method of claim 6, comprising: a first disc type recognizing
step for determining, depending on how long it has taken for the
number of revolutions of a motor that rotates the optical disc to
reach a predetermined number, whether the optical disc loaded is a
lightweight disc or not; and a second disc type recognizing step
for determining, based on a signal that has been obtained from the
disc loaded, whether the optical disc is an 8 cm disc or a 12 cm
disc, and wherein if the optical disc loaded has been determined to
be a lightweight disc and a 12 cm disc as a result of the first and
second disc type recognizing steps, respectively, then the optical
disc loaded is recognized to be a slim disc.
9. The method of claim 6, comprising: a first disc type recognizing
step for determining, depending on how long it has taken for the
number of revolutions of a motor that rotates the optical disc to
reach a predetermined number, whether the optical disc loaded is a
lightweight disc or not; and a second disc type recognizing step
for determining, based on a signal that has been obtained from the
disc loaded, whether the optical disc is an 8 cm disc or a 12 cm
disc, and wherein if the optical disc loaded has been determined to
be a lightweight disc and a 12 cm disc as a result of the first and
second disc type recognizing steps, respectively, then it is
determined that disc slippage has occurred.
10. The method of claim 8, wherein the second disc type recognizing
step includes the steps of: if the optical disc has been determined
to be an 8 cm disc, moving an optical head to a radial location
outside of a data area; and if either the surface or a storage
layer of the optical disc loaded has been detected by a focus error
signal, determining the optical disc loaded to be a 12 cm disc.
11. The method of claim 8, wherein the second disc type recognizing
step includes the steps of: retrieving identification information
of the optical disc from the optical disc loaded; and determining,
by reference to disc size information included in the
identification information, whether the optical disc is a 12 cm
disc or not.
12. The method of claim 8, further comprising a third disc type
recognizing step for determining the optical disc loaded to be a
slim disc if a signal obtained from the optical disc loaded
indicates that the axial runout of the optical disc is greater than
a predetermined value.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an optical disc drive for
reading data from an optical disc loaded and also relates to a
method for recognizing the type of the optical disc loaded.
[0003] 2. Description of the Related Art
[0004] Various types of optical discs, including Blu-ray Discs
(BDs), DVDs and CDs, are currently available but not all of them
have the same size. Some of them have a diameter of 12 cm (and will
be referred to herein as "12 cm discs") and others have a diameter
of 8 cm (and which will be referred to herein as "8 cm discs").
That is why when loaded with an optical disc, an optical disc drive
needs to change the position to emit a light beam from according to
the size of the disc, and therefore, has to decide whether the disc
loaded is a 12 cm disc or an 8 cm disc. Such a disc type
recognition process will be referred to herein as "12 cm/8 cm disc
type recognition".
[0005] In general, a 12 cm disc has a greater moment of inertia
than an 8 cm disc. In other words, a 12 cm disc is less easy to
rotate than an 8 cm disc. That is to say, the moment of inertia of
an object is a quantity indicating how difficult it is to rotate
that object. Supposing two discs are made of the same material and
have the same thickness, one of the two discs with the longer
diameter should have the greater moment of inertia than the other
disc with the shorter diameter. For that reason, if the 12 cm disc
and 8 cm disc are rotated separately with the same voltage applied
to the same disc motor, it will take a longer time for the 12 cm
disc to increase its number of revolutions to the target one than
the 8 cm disc does. In view of these considerations, according to a
conventional 12 cm/8 cm disc type recognition process, the optical
disc loaded is determined to be either a cm disc or an 8 cm disc by
paying special attention to their difference in moment of inertia.
Specifically, for that purpose, with the same voltage applied to a
disc motor that rotates those optical discs separately, it is
measured how long it takes for the disc motor to increase its
number of revolutions to a predetermined one with the disc mounted,
and the type of the disc loaded is recognized by the length of that
time it has taken. See Japanese Patent Application Laid-Open
Publication No. 2003-249004, for example (which will be referred to
herein as "Patent Document No. 1" for convenience sake).
[0006] According to the method disclosed in Patent Document No. 1,
however, a so-called "slim disc" or "eco disc" (which will be
collectively referred to herein as a "slim disc" and) which has
become more and more popular year by year cannot be properly
distinguished from an 8 cm disc. As will be described later, a slim
disc certainly has a smaller thickness but does have a diameter of
12 cm. Also, apart from the thickness, a slim disc has quite the
same physical structure (including a pit size and a track
structure) as a normal DVD-ROM (which is a 12 cm disc). An example
of such a slim disc is disclosed in United States Patent
Application Publication No. 2008/0115156.
[0007] A slim disc has a thinner substrate and a lighter weight.
That is why if a slim disc is loaded into an optical disc drive and
rotated by its disc motor, it will take a shorter amount of time
for the disc motor, to which the same difference is applied, to
increase its number of revolutions to a predetermined one than when
a normal 12 cm disc is loaded to it. For that reason, even though
the slim disc is actually a 12 cm disc, it could be taken for an 8
cm disc by mistake, which is a problem.
[0008] Also, as a slim disc has a thinner substrate, the slim disc
is more likely to cause a disc flutter (which is also called an
"axial runout or deflection" or "surface runout") which is a
variation in height as measured along the circumference of the
disc. For that reason, it is more difficult to get servo controls
done with good stability during reading than when a disc with a
normal thickness is loaded, and therefore, the disc drive needs to
decide whether the disc loaded is a slim disc or not. Nevertheless,
no information indicating its identity as a slim disc is recorded
on a slim disc, which just carries disc identification information
indicating that it is a DVD-ROM. Consequently, there is a growing
demand for a more accurate disc type recognition method for
determining, without relying on the disc identification
information, whether the disc loaded is a slim disc or not.
[0009] It is therefore an object of the present invention to
provide an optical disc drive that can perform a read operation
with stability even on a slim disc and also provide a method for
reading data from such an optical disc.
SUMMARY OF THE INVENTION
[0010] An optical disc drive according to the present invention can
read data from both a normal thickness disc, which has a thickness
of 1.2 mm and that has stored data thereon, and a slim disc, which
has a thickness of 1.0 mm or less and that has also stored data
thereon. The drive includes: a motor for rotating a disc loaded; an
optical head for focusing a light beam on the disc that is being
rotated by the motor; and a control section for controlling the
operations of the motor and the optical head. When reading data
from the slim disc, the control section makes the motor or the
optical head operate under a different operating condition than
when reading data from the normal thickness disc.
[0011] In one preferred embodiment of the present invention, the
operating condition includes at least one of the number of
revolutions of the motor, the gain of a focus control, and a radial
location on the disc at which the light beam that irradiates the
disc needs to be focused.
[0012] In another preferred embodiment, the control section
includes a disc type recognition section for determining whether
the disc loaded is a slim disc or not.
[0013] In still another preferred embodiment, if the disc loaded is
the slim disc, the control section raises the lower limit of the
number of revolutions of the motor.
[0014] In yet another preferred embodiment, if data cannot be read
properly from the disc loaded by operating the motor and the
optical head under an operating condition for reading the data from
the normal thickness disc, at least a part of that operating
condition is changed into an operating condition for reading data
from the slim disc.
[0015] An optical disc reading method according to the present
invention is a method for reading data from an optical disc loaded
by using an optical disc drive that is compatible with both a
normal thickness disc, which has a thickness of 1.2 mm and that has
stored data thereon, and a slim disc, which has a thickness of 1.0
mm or less and that has also stored data thereon. The method
includes the steps of: rotating the optical disc loaded;
irradiating the optical disc with a light beam; and if the optical
disc loaded is the slim disc, making the optical disc drive operate
under a different operating condition from when reading data from
the normal thickness disc.
[0016] In one preferred embodiment of the present invention, the
method includes a disc type recognizing step for determining
whether the disc loaded is the slim disc or not.
[0017] In another preferred embodiment, the method includes: a
first disc type recognizing step for determining, depending on how
long it has taken for the number of revolutions of a motor that
rotates the optical disc to reach a predetermined number, whether
the optical disc loaded is a lightweight disc or not; and a second
disc type recognizing step for determining, based on a signal that
has been obtained from the disc loaded, whether the optical disc is
an 8 cm disc or a 12 cm disc. If the optical disc loaded has been
determined to be a lightweight disc and a 12 cm disc as a result of
the first and second disc type recognizing steps, respectively,
then the optical disc loaded is recognized to be a slim disc.
[0018] In an alternative preferred embodiment, the method includes:
a first disc type recognizing step for determining, depending on
how long it has taken for the number of revolutions of a motor that
rotates the optical disc to reach a predetermined number, whether
the optical disc loaded is a lightweight disc or not; and a second
disc type recognizing step for determining, based on a signal that
has been obtained from the disc loaded, whether the optical disc is
an 8 cm disc or a 12 cm disc. If the optical disc loaded has been
determined to be a lightweight disc and a 12 cm disc as a result of
the first and second disc type recognizing steps, respectively,
then it is determined that disc slippage has occurred.
[0019] In this particular preferred embodiment, the second disc
type recognizing step includes the steps of: if the optical disc
has been determined to be an 8 cm disc, moving an optical head to a
radial location outside of a data area; and if either the surface
or a storage layer of the optical disc loaded has been detected by
a focus error signal, determining the optical disc loaded to be a
12 cm disc.
[0020] In a specific preferred embodiment, the second disc type
recognizing step includes the steps of: retrieving identification
information of the optical disc from the optical disc loaded; and
determining, by reference to disc size information included in the
identification information, whether the optical disc is a 12 cm
disc or not.
[0021] In another specific preferred embodiment, the method further
includes a third disc type recognizing step for determining the
optical disc loaded to be a slim disc if a signal obtained from the
optical disc loaded indicates that the axial runout of the optical
disc is greater than a predetermined value.
[0022] In this particular preferred embodiment, the third disc type
recognizing step includes the steps of: moving the optical head to
a radial location in an outer area of a 12 cm disc; and measuring
the amount of focus drive current that has flowed while the disc
makes one turn with a focus control turned ON and determining, by
the amount of the focus drive current, whether the optical disc
loaded is a slim disc or not.
[0023] In a specific preferred embodiment, the method includes the
step of measuring the amounts of the focus drive current that flows
when the number of revolutions of the motor is large and when the
number of revolutions of the motor is small, respectively, and
determining the optical disc loaded to be a slim disc if the
difference between the amounts of current measured in those two
situations is greater than a predetermined value.
[0024] In yet another preferred embodiment, the method further
includes the step of controlling the number of revolutions to a
certain value or more in order to minimize the influence of the
axial runout if the optical disc loaded has turned out to be a slim
disc as a result of the third disc type recognizing step.
[0025] In yet another preferred embodiment, the method further
includes the step of carrying out an error recovery process in
order to minimize the influence of the axial runout if the optical
disc loaded has turned out to be a slim disc as a result of the
third disc type recognizing step.
[0026] In yet another preferred embodiment, the method further
includes the step of outputting an alert that prompts the user to
clean a disc turntable if the optical disc loaded has turned out to
be a non-slim disc as a result of the third disc type recognizing
step.
[0027] In yet another preferred embodiment, the method further
includes the step of controlling the number of revolutions to a
certain value or more in order to minimize the influence of the
axial runout if the optical disc loaded has turned out to be a slim
disc as a result of the first and second disc type recognizing
steps.
[0028] In yet another preferred embodiment, the method further
includes the step of carrying out an error recovery process in
order to minimize the influence of the axial runout if the optical
disc loaded has turned out to be a slim disc as a result of the
first and second disc type recognizing steps.
[0029] In yet another preferred embodiment, the method further
includes the step of outputting an alert that prompts the user to
clean a disc turntable if it has turned out as a result of the
first and second disc type recognizing steps that disc slippage has
occurred.
[0030] In yet another preferred embodiment, the method further
includes the step of decreasing acceleration, with which the disc
in rest position starts to be rotated from next time on, if it has
turned out as a result of the first and second disc type
recognizing steps that disc slippage has occurred.
[0031] In yet another preferred embodiment, the method further
includes the step of increasing a clamping force, with which the
disc in rest position starts to be rotated from next time on, if it
has turned out as a result of the first and second disc type
recognizing steps that disc slippage has occurred.
[0032] According to the present invention, when loaded with a slim
disc, the optical disc drive operates under a different operating
condition from when loaded with a normal thickness disc, thereby
performing a read operation with good stability even on the slim
disc that has less rigidity, and will produce a greater axial
runout, than the normal thickness disc.
[0033] Other features, elements, processes, steps, characteristics
and advantages of the present invention will become more apparent
from the following detailed description of preferred embodiments of
the present invention with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1(a) is a top view of an optical disc 101 and FIG. 1(b)
is a schematic cross-sectional view thereof.
[0035] FIGS. 2(a), 2(b) and 2(c) are schematic cross-sectional
views illustrating a 12 cm disc, an 8 cm disc, and a slim disc,
respectively.
[0036] FIG. 3 is a block diagram illustrating an exemplary
configuration for an optical disc drive according to the present
invention.
[0037] FIG. 4 is a block diagram illustrating a detailed
configuration for the optical disc drive of the first preferred
embodiment.
[0038] FIG. 5 is a flowchart showing the overall procedure of
determining what type of optical disc has been loaded into the
optical disc drive according to the first preferred embodiment of
the present invention.
[0039] FIG. 6 is a flowchart showing how to recognize the type of
the disc loaded based on the time it takes for the number of
revolutions to reach a target number according to the first
preferred embodiment of the present invention.
[0040] FIG. 7 is a graph showing how the number of revolutions of a
disc motor 102 changes with the amount of time that has passed
since the motor 102 started to rotate with an optical disc mounted
thereon.
[0041] FIG. 8 is a flowchart showing how to recognize the type of
the disc loaded based on a signal detected from the disc according
to the first preferred embodiment of the present invention.
[0042] FIG. 9 is a flowchart showing how to recognize the type of
the disc loaded based on not only the time it takes for the number
of revolutions to reach a target number but also a signal detected
from the disc according to the first preferred embodiment of the
present invention.
[0043] FIG. 10 is a graph showing how the number of revolutions
changes according to the radial location on an optical disc on
which a read operation is being performed.
[0044] FIG. 11 shows how a lower limit may be set to the number of
revolutions by 3.times.CLV or 2.times.CLV.
[0045] FIGS. 12(a), 12(b) and 12(c) are schematic representations
illustrating a disc that rotates with an axial runout according to
the first preferred embodiment of the present invention.
[0046] FIG. 13 is a flowchart showing how to recognize the type of
such a disc rotating with an axial runout as shown in FIG. 12
according to the first preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0047] FIG. 1(a) is a top view of an optical disc 101 and FIG. 1(b)
is a schematic cross-sectional view thereof. The optical disc 101
includes a disklike substrate, which is axisymmetric with respect
to the center C of the disc, and one or multiple storage layers
(not shown) that is/are supported on the substrate. As shown in
FIGS. 1(a) and 1(b), the optical disc 101 has a clamp area 20,
which covers the disc center C and its neighboring area, and a data
area 30, which surrounds the clamp area 20. Alternatively, the
clamp area 20 may also be defined to cover only the range between
the disc center hole and the data area 30 with the disc center hole
excluded.
[0048] FIGS. 2(a), 2(b) and 2(c) are schematic cross-sectional
views illustrating a 12 cm disc (such as a DVD-ROM), an 8 cm disc,
and a slim disc, respectively. The measurements of these optical
discs illustrated on the paper are not to scale and do not
represent their actual sizes, either.
[0049] In the following description and in the claims of the
present application, a normal 12 cm disc and a normal 8 cm disc
will be collectively referred to herein as "normal thickness
discs". As used herein, a "normal thickness disc" has a disklike
portion that has a thickness of 1.2 mm and that has stored data on
its data area 30. In this case, the data area 30 is too rigid to
warp easily. Normal 12 cm discs and 8 cm discs are included in
normal thickness discs. On the other hand, a "slim disc" has a
disklike portion that has a thickness of 1.0 mm or less and that
has stored data on its data area 30. As shown in FIG. 2(c), the
clamp area 20 of the slim disc has the same thickness of 1.2 mm as
the counterpart of the normal thickness discs. However, the data
area 30 that forms a major part of the slim disc is thinner than
usual. As a result, the overall weight of the slim disc is lighter
than those of normal thickness discs. The data area 30 of a slim
disc is usually not rigid enough to avoid a warp. The data area 30
may have a thickness of 0.6 mm, for example, which could be either
decreased or increased. As used herein, the "slim discs" include
discs with any other thickness or weight as long as their thickness
or weight is less than that of normal 12 cm discs.
[0050] The present invention relates to an optical disc drive that
can read data from both a normal thickness disc and a slim disc. As
shown in FIG. 3, the optical disc drive of the present invention
includes a motor (also called a "disc motor") 102 for rotating the
disc 101 loaded, an optical head (also called an "optical pickup")
103 for focusing a light beam on the disc 101 that is being rotated
by the motor 102, and a control section 40 for controlling the
operations of the motor 102 and the optical head 103.
[0051] When reading data from a slim disc, the control section 40
makes the motor 102 and the optical head 103 operate under a
different operating condition than when reading data from a normal
thickness disc. This "operating condition" includes the number of
revolutions of the motor 102, the gain of a focus control, and a
radial location on the disc to be irradiated with the light beam.
That is to say, depending on whether the optical disc 101 loaded is
a normal thickness disc or a slim disc, at least one of the
operating condition parameters, including the number of revolutions
of the motor 102, the focus control gain, and a radial location to
be irradiated with the light beam, is changed. For example, if the
optical disc loaded has turned out to be a slim disc, the number of
revolutions of the motor may be increased compared to the setting
for a normal thickness disc. As a result, the warp of a slim disc,
which is not rigid enough to avoid warping, can be minimized by
rotating it at a high frequency. On top of that, by controlling the
operating condition adaptively to a slim disc, read errors can be
reduced significantly, too.
[0052] In one preferred embodiment of the present invention, the
control section 40 includes a disc type recognition section 50 for
determining whether the disc 101 loaded is a slim disc or not. If
the disc type recognition section 50 has recognized the disc 101
loaded to be a slim disc, the control section 40 may raise the
lower limit of the number of revolutions of the motor 102, for
example.
[0053] Nevertheless, the optical disc drive does not always have to
include such a disc type recognition section 50. If an optical disc
drive without such a disc type recognition section 50 has operated
the motor and the optical head under such an operating condition
for reading data from a normal thickness disc only to fail to read
data properly from the disc 101 loaded, then at least a part of
that operating condition may be changed into one for reading data
from a slim disc. This is because if data cannot be read properly
from the optical disc 101 loaded by operating the motor 102 and the
optical head 103 under such an operating condition for reading data
from a normal thickness disc, probably the disc 101 loaded is a
slim disc.
[0054] Hereinafter, preferred embodiments of the present invention
will be described with reference to the accompanying drawings.
[0055] FIG. 4 is a block diagram illustrating a configuration for
an optical disc drive 100 as first specific preferred embodiment of
the present invention.
[0056] As shown in FIG. 4, the optical disc drive 100 includes a
turntable 111, a disc motor 102, a disc clamper 110, an optical
head 103, a transport section 109, a signal processing section 104,
a laser control section 105, a servo section 106, and a system
control section 107. The turntable 111 is provided to mount an
arbitrary optical disc 101 (which may be a Blu-ray Disc, for
example) thereon, and is secured to a shaft and turned by the disc
motor 102. When the disc 101 is loaded into this optical disc drive
100, the disc clamper 110 clamps the disc 101 onto the turntable
111 and the optical head 103 irradiates the disc 101 with a laser
beam. To start an actual read operation, the transport section 109
(such as a traverse motor) moves the optical head 103 to a target
radial location on the disc 101. Then, the read signal generated by
the optical head 103 is binarized by the signal processing section
104, which also generates a clock signal to synchronize the timings
of operations of these components. To get the read operation done
properly, the laser control section 105 controls the power and
pulse width of a laser beam emitted from the optical head 103,
while the servo section 106 controls the number of revolutions of
the disc motor 102 and the operation of the optical head 103. To
perform an overall control on this optical disc drive 100, the
system control section 107 sets the laser power for the laser
control section 105, and issues a control command to the servo
section 106. The system control section 107 interprets the signal
supplied from the signal processing section 104, thereby decoding
the data that has been obtained from the optical disc 100.
[0057] The system control section 107 includes a slim disc
recognizing section 108 for determining, by the number of
revolutions of the optical disc 101 and the signal obtained from
the optical disc 101, whether the optical disc 101 loaded is a slim
disc or not. A nonvolatile memory 112 that stores various sorts of
information, including information about what kinds of errors have
occurred in the optical disc drive 100 so far, is also included in
the system control section 107.
[0058] In the optical disc drive 100 of this preferred embodiment,
the slim disc recognizing section 108 is built in the system
control section 107. However, the slim disc recognizing section 108
may also be either provided as an independent functional block in
this optical disc drive 100 or even built in any other circuit
section.
[0059] The signal processing section 104, the laser control section
105, the servo section 106 and the system control section 107 may
be implemented as either hardware circuits only or a combination of
a software program and hardware circuits. Specifically, the
function of each of these sections is preferably carried out by one
or multiple processors manufactured by integrated circuit
technologies and a program that is defined to control the operation
of that/those processor(s). In this preferred embodiment, the
system control section 107 and the slim disc recognizing section
108 are supposed to instruct the laser control section 105 and the
servo section 106 what to do by issuing commands for them.
[0060] Hereinafter, it will be described in detail with reference
to a flowchart exactly how the slim disc recognizing section 108
recognizes a slim disc. First off, look at FIG. 5, which is a
flowchart showing the overall procedure of determining what type of
optical disc has been loaded into this optical disc drive 100.
[0061] As shown in FIG. 5, in Step 201, on sensing that an optical
disc 101 has been loaded, the slim disc recognizing section 108
issues a control command to the servo section 106, makes the disc
motor 102 rotate the optical disc 101, and then measures, using a
timer (not shown), how long it has taken for the number of
revolutions of the disc motor 102 to reach a target number. Then,
by comparing this waiting time measured to a preset reference time,
the slim disc recognizing section 108 determines whether the disc
loaded in Step 201 is a normal 12 cm disc or a lightweight disc,
which has a lighter weight than the normal 12 cm disc. As used
herein, the "lightweight disc" refers to either an 8 cm disc or a
slim disc. In any case, the moment of inertia of a lightweight disc
is so much smaller than that of a 12 cm disc that a lightweight
disc can be rotated easily by the motor. That is why if the disc
loaded is a lightweight disc, the number of revolutions of the
motor should reach the target number in a shorter time than a
situation where the disc loaded is a 12 cm disc. Thus, if the time
it has taken for the number of revolutions of the motor to reach
the target one is actually measured and compared to an
appropriately set reference time, the optical disc loaded can be
easily determined to be either a lightweight disc or a normal 12 cm
disc.
[0062] In this preferred embodiment, the reference time to decide
whether the disc loaded is a lightweight disc or not is set to be
100 ms. However, this is only an example and the reference time may
also be changed into any other value according to the structure of
the motor or any other factor. It will be described later exactly
how to set the reference time.
[0063] Hereinafter, it will be described in further detail with
reference to FIG. 6 specifically how this processing step 201 is
carried out. FIG. 6 is a flowchart showing an exemplary detailed
procedure through which the optical disc drive 100 performs a disc
type recognition process by detecting the amount of time it has
taken for the number of revolutions of the motor to reach a target
one.
[0064] In the example shown in FIG. 6, first of all, in Step 301,
the slim disc recognizing section 108 issues a command to the servo
section 106, thereby setting the target number of revolutions of
the disc motor 102 to be 1,000 rpm. Next, in Step 302, using a
timer (not shown), the slim disc recognizing section 108 measures
the amount of time it has taken for the number of revolutions of
the disc motor 102 to actually reach 1,000 rpm under the control of
the servo section 106. Although the target number of revolutions is
set to be 1,000 rpm in this example, the target number may also be
set to be any other value as well.
[0065] Next, in Step 303, the slim disc recognizing section 108
determines whether or not the waiting time measured in the previous
processing step 302 is less than 100 ms, which is a reference time.
If the answer is YES (i.e., waiting time <100 ms), the process
advances to Step 304, in which the disc loaded is recognized to be
a lightweight disc. Otherwise (i.e., waiting time .gtoreq.100 ms),
the process advances to Step 305, in which the disc loaded is
recognized to be a normal 12 cm disc. It should be noted that the
number of revolutions of the disc motor 102 to be set in Step 301
and the reference time for use to make the decision in Step 303 may
be any arbitrary values as long as the disc loaded can be
determined to be either a lightweight disc or a normal 12 cm
disc.
[0066] Hereinafter, the relation between the number of revolutions
of the motor and the running time will be described with reference
to FIG. 7, which is a graph showing how the number of revolutions
of the disc motor 102 changes with the amount of time that has
passed since the motor 102 started to rotate with the optical disc
mounted thereon. In FIG. 7, the curves B101, B102 and B103
represent data that was collected from an 8 cm disc, a slim disc
and a normal 12 cm disc, respectively.
[0067] It took 60 ms, 95 ms and 140 ms for the number of
revolutions to reach 1,000 rpm in the cases of the 8 cm disc, slim
disc and normal 12 cm disc, respectively. In this manner, it will
take a different amount of time for the number of revolutions of
the motor to reach the target one according to the type of the
optical disc loaded because these three types of optical discs have
mutually different moments of inertia. The reference time for use
to determine the type of the disc loaded in Step 303 shown in FIG.
6 may be set to be an arbitrary value between 95 ms and 140 ms.
[0068] Now look at FIG. 5 again. If the optical disc 101 loaded has
been recognized to be a normal 12 cm disc (e.g., a DVD-ROM) in Step
202 shown in FIG. 5, then the disc type recognition process ends.
On the other hand, if the disc loaded has turned out to be a
lightweight disc, then the process advances to Step 203.
[0069] In Step 203, based on the signal that has been detected by
the optical head 103 from the optical disc 101, the slim disc
recognizing section 108 determines whether the disc loaded is an 8
cm disc or a slim disc.
[0070] Hereinafter, it will be described in further detail with
reference to FIG. 8 exactly how this processing step 203 is carried
out. FIG. 8 is a flowchart showing the procedure through which the
optical disc drive 100 performs a disc type recognition based on
the signal received from the disc. First of all, in Step 401, the
slim disc recognizing section 108 issues a command to the servo
section 106, thereby instructing the transport section 109 to move
the optical head 103 to a radial location of 50 mm on the optical
disc 101. It should be noted that the location to which the optical
head 103 is moved in this processing step does not have to be a
radial location of 50 mm but may also be any other location as long
as at that location, there is no disc surface or storage layer of
an 8 cm disc but there is either the disc surface or a storage
layer of a 12 cm disc.
[0071] Next, in Step 402, the slim disc recognizing section 108
issues a command to the servo section 106 to make the optical head
103 detect either the disc surface or a storage layer using a focus
error signal.
[0072] If it has turned out in Step 403 that any disc surface or
any storage layer has been detected in the processing step 402, the
process advances to Step 405, in which the disc loaded is
recognized to be a 12 cm disc. On the other hand, if it has turned
out in Step 403 that no disc surface or storage layer has been
detected in the processing step 402, then the process advances to
Step 404, in which the disc loaded is recognized to be an 8 cm
disc. Since no disc surface or storage layer can be detected if the
disc loaded is an 8 cm disc, the disc loaded can be determined to
be either an 8 cm disc or a 12 cm disc without fail according to
this method.
[0073] Now look at FIG. 5 once again. If the optical disc loaded
101 has turned out to be an 8 cm disc in Step 204 shown in FIG. 5,
the disc type recognition process ends. On the other hand, if the
optical disc loaded 101 has turned out to be a non-8 cm disc (i.e.,
a 12 cm disc), then the process advances to Step 205.
[0074] In this manner, according to this preferred embodiment, if
the disc loaded has turned out in Step 204 to be a non-8 cm disc,
the process advances to Step 205 to decide whether the optical disc
loaded is a slim disc or not. This needs to be done because even if
the disc loaded is not a slim disc but actually a normal 12 cm
disc, that disc could be taken for a lightweight disc by mistake in
Step 202. Optionally, instead of making such a strict decision, if
the disc loaded has turned out to be a non-8 cm disc in Step 204,
then that disc may be determined to be an 8 cm disc automatically
to omit the processing steps 205 and 206. In that case, the process
advances to Step 207 of setting a lower limit to the number of
revolutions of the motor. According to this modified example, even
a non-slim disc could be recognized to be a slim disc by mistake.
Nevertheless, as far as the read operation is concerned, there
should be no problem at all. Rather the read operation can be
carried out with more stability by setting a lower limOit to the
number of revolutions in Step 207.
[0075] According to this preferred embodiment, if the optical disc
loaded has turned out in Step 204 to be a non-8 cm disc (i.e., a 12
cm disc), it may be determined that disc slippage has occurred. As
will be described later, even if the disc loaded is a normal 12 cm
disc, the number of revolutions of the motor could reach its target
number in a short time due to disc slippage. In that case, this
procedure may be modified so that the process advances to Step 208
of displaying information about disc slippage with the processing
steps 205 and 206 skipped. It is known that since a slim disc is
heavier than an 8 cm disc, the number of revolutions of the motor
on which a slim disc is mounted should reach, considering its
moment of inertia, a predetermined value later than when the disc
loaded is an 8 cm disc and earlier than when the disc loaded is a
12 cm disc (see FIG. 7). That is why in this modified example, even
if the disc loaded is a slim disc, it can still be determined
properly whether or not disc slippage has occurred by setting a
decision threshold value between the time it takes for the motor
with an 8 cm disc to reach a predetermined number of revolutions
and the time it takes for the motor with a slim disc to reach it in
Step 303 shown in FIG. 6. According to the data shown in FIG. 7,
for example, the decision threshold value may be set somewhere
between 60 ms and 95 ms. This modified example is applicable
particularly effectively to a system that can perform a read
operation with good stability even on a slim disc loaded without
taking any special measures against its axial runout (e.g., a
system in which the motor can always rotate at 2,000 rpm or more
during reading).
[0076] According to this preferred embodiment, unless any of those
simplified processes is adopted, the slim disc recognizing section
108 determines, in Step 205 shown in FIG. 5, by reference to the
information provided by the servo section 106 or the signal
processing section 104, whether the disc loaded is a slim disc or
not.
[0077] Hereinafter, it will be described in further detail with
reference to FIG. 9 specifically how this processing step 205 is
performed. FIG. 9 is a flowchart showing a procedure through which
the optical disc drive 100 decides, by reference to the information
provided by the servo section 106 or the signal processing section
104, whether the disc loaded is a slim disc or not. It should be
noted that the series of processing steps shown in FIG. 9 are
supposed to be started when the disc is already rotating. Thus, if
the disc has not started rotating yet, the servo section 106 is
instructed to rotate the disc motor 102 before the processing step
501 starts to be performed.
[0078] First, in Step 501, the signal processing section 104
processes the signal supplied from the optical head 103, thereby
obtaining disc identification information from the optical disc
101. As used herein, the disc identification information refers to
the information that is stored in the control data area of a disc
to indicate the type, storage capacity, and size (which may be
either 8 cm or 12 cm) of the disc.
[0079] Next, in Step 502, it is determined, by reference to the
information that has been obtained in the previous processing step
501, whether the disc loaded is a DVD-ROM or not. If the answer is
NO, the process advances to Step 508 in which the disc loaded is
determined to be a non-slim disc. On the other hand, if the answer
is YES, then the process advances to Step 503 to continue this
process.
[0080] Subsequently, as in Step 401, the slim disc recognizing
section 108 issues a command in Step 503 to the servo section 106,
thereby instructing the transport section 109 to move the optical
head 103 to a radial location of 50 mm on the optical disc 101. It
should be noted that the location to which the optical head 103 is
moved in this processing step does not have to be a radial location
of 50 mm but may also be any other location where the axial runout
of the disc can be detected. Also, if the focus control needs to be
turned OFF when the optical head 103 is moved, then this processing
step 503 is performed after having turned the focus control
OFF.
[0081] Thereafter, in Step 504, the slim disc recognizing section
108 issues a command to the servo section 106 to turn the focus
control on the optical disc 101 ON. Then, in Step 505, the slim
disc recognizing section 108 issues another command to the servo
section 106 to get the amount of focus drive current that has
flowed while the disc makes one turn, thereby measuring the
magnitude of the axial runout of the optical disc 101.
[0082] Next, if the variation in focus drive current that has been
measured in the previous processing step 505 corresponds to an
axial runout of 0.3 mm or more at the outer edge of the disc, for
example, then the disc loaded is determined in Step 506 to have
caused a significant axial runout and recognized to be a slim disc
in Step 507. On the other hand, if the disc loaded is determined in
Step 506 to have caused no significant axial runout, then the
process advances to Step 508 in which the disc loaded is recognized
to be a non-slim disc. It should be noted that the threshold value
for use to decide whether the axial runout is significant or not
does not have to be 0.3 mm but may be arbitrarily set by the
designer because the magnitude of the axial runout varies with the
coil resistance and other factors and may or may not be allowable
depending on what kind of system is used.
[0083] Also, the measuring processing step 505 may be carried out
at multiple different numbers of revolutions (e.g., at a relatively
small number of revolutions of 800 rpm and at a relatively large
number of revolutions of 2,000 rpm). And if the results of these
measurements are quite different, then it may be determined in Step
506 that the axial runout is significant.
[0084] Now let's go back to the flowchart shown in FIG. 5. If it
has turned out in Step 206 that the optical disc loaded 101 is a
slim disc, then the system control section 107 sets in the next
processing step 207 the lower limit of the number of revolutions of
the optical disc 101 to be at least 1,500 rpm, thereby minimizing
the axial runout of the disc with the centrifugal force of the disc
rotating increased.
[0085] Hereinafter, it will be described with reference to FIG. 10
exactly how to set a lower limit to the number of revolutions in
Step 207. FIG. 10 is a graph showing how the number of revolutions
changes according to the radial location on an optical disc on
which a read operation is being performed.
[0086] In the following example, the number of revolutions of an
optical disc is supposed to be controlled by one of CAV (constant
angular velocity) and CLV (constant linear velocity) methods, which
are two major methods for controlling the number of revolutions of
optical discs.
[0087] As indicated by the lines A103 and A104, according to the
CAV method, the number of revolutions is always constant
irrespective of the radial location. In FIG. 10, the lines A103 and
A104 indicate the results obtained by adopting a 4.times.CAV method
and a 2.times.CAV method, respectively.
[0088] On the other hand, according to the CLV method, the number
of revolutions is changed with the radial location to keep the
relative velocity of the disc with respect to the optical head
constant as indicated by the curves A101 and A102. In FIG. 10, the
curves A101 and A102 indicate the results obtained by adopting a
3.times.CLV method and a 2.times.CLV method, respectively.
[0089] Next, it will be described with reference to FIG. 11 how to
set a lower limit to the number of revolutions by the CLV method.
FIG. 11 shows how a lower limit may be set to the number of
revolutions by 3.times.CLV or 2.times.CLV. In FIG. 11, the curve
C101 shows how the number of revolutions changes with the radial
location according to the 3.times.CLV method, while the curve C102
shows how the number of revolutions changes with the radial
location according to the 2.times.CLV method.
[0090] If the number of revolutions of the optical disc is
controlled by 3.times.CLV, the number of revolutions is always
equal to or greater than 1,500 rpm at every radial location as
indicated by the curve C101, and therefore, there is no need to
change the modes of control. On the other hand, if the number of
revolutions of the optical disc is controlled by 2.times.CLV, the
number of revolutions is less than 1,500 rpm at radial locations
that are closer to the disc outer edge than a radial location C104
(of approximately 44.5 mm) is, at which the number of revolutions
is 1,500 rpm. That is why if the disc loaded has turned out to be a
slim disc, a lower limit can be set to the number of revolutions by
controlling the number of revolutions as indicated by the line
C103.
[0091] If the number of revolutions is controlled by the CAV
method, the number of revolutions is always constant irrespective
of the radial location. That is why if the optical disc loaded has
turned out to be a slim disc while its number of revolutions is
controlled by 2.times.CAV, by which the number of revolutions would
usually be less than 1,500 rpm as indicated by the line A104 in
FIG. 10, then the rates of the CAV control may be changed (into
4.times.CAV as indicated by the line A103) so as to increase the
number of revolutions to more than 1,500 rpm.
[0092] It should be noted that the rates of control may also be
changed into any other rate as long as the number of revolutions
can be increased to more than 1,500 rpm. For instance, even a
number of revolutions control method of a different mode (such as
3.times.CLV as indicated by the curve A101 in FIG. 10) could also
be used.
[0093] Optionally, instead of always setting a lower limit to the
number of revolutions, the lower limit could be set only when a
recovery process needs to be done in order to remove an error that
has occurred during reading, for example.
[0094] Let's go back to FIG. 5. If the disc loaded has turned out
to be a non-slim disc in Step 206 shown in FIG. 5, then it is
determined that disc slippage (i.e., misalignment of the disc) has
occurred and information about the disc slippage is output to a
display section (not shown) in Step 208. It can be determined in
this processing step 208 that disc slippage have occurred because
the disc loaded has turned out to be a lightweight disc in Step 202
and yet has been recognized to be neither an 8 cm disc (in Step
204) nor a slim disc (in Step 206). That is to say, it can be
determined that optical disc have been loaded improperly (i.e.,
slips) in that case.
[0095] Thus, in this processing step 208, an alert saying "please
use disc turntable cleaner", for example, may be displayed on the
monitor screen of a TV, to which this optical disc drive 100 is
connected. As used herein, the disc turntable 111 is a table for
rotating the optical disc 101 that is mounted thereon. While the
disc 101 is rotating, the disc turntable 111 is located under the
clamp area and is also turning along with the disc 101. If the
turntable 111 has gathered dust, for example, the disc 101 will
slip easily.
[0096] As to when to output such information about the disc
slippage, information about the number of times disc slippage has
occurred so far may be stored in the nonvolatile memory 112 and may
be displayed only when the number of times of occurrence exceeds a
predetermined number. Or that information may also be output when
an error is indicated as a result of an analysis that has been made
at the time of a failure.
[0097] Furthermore, if disc slippage has occurred, the
acceleration, with which the disc in rest position starts to be
rotated from next time on, may be decreased or a clamp force, with
which the disc starts to be rotated from next time on, may be
increased so that such disc slippage will never happen again. Also,
if the disc loaded has turned out to be a slim disc, it is not
always necessary to set a lower limit to the number of revolutions
but any other measure may also be taken to perform a servo control
with good stability on a disc that is producing a significant axial
runout. Examples of such countermeasures include increasing the
gain of the focus control, performing a retry (i.e., an error
recovery process) on an inner area of the disc (e.g., inside of a
radial location of 40 mm) to be affected less by the axial runout,
moving the objective lens toward the disc more slowly when the
focus needs to be set on an outer area of the disc (e.g., outside
of a radial location of 50 mm), and changing the modes of control
of the servo section 106 according to the angle of the disc that
corresponds to one period of the axial runout of the disc.
[0098] In any case, by performing these processing steps, it can be
determined whether the optical disc loaded is a slim disc or not,
and the servo control can be performed with good stability.
[0099] Alternative Decision Steps for Step 205 shown in FIG. 5
(Consisting of Processing Steps shown in FIG. 9)
[0100] FIG. 12(a) is a perspective view illustrating a slim disc,
while FIGS. 12(b) and 12(c) are cross-sectional views thereof as
respectively viewed on the planes a-b and c-d shown in FIG. 12(a).
As can be seen from FIGS. 12(a), 12(b) and 12(c), this slim disc is
warped along the dashed line that connects the points a and b
together with respect to a ridge indicated by the dashed line that
connects the points c and d together. Even if the level of the
storage layer has varied by a matter of several .mu.m due to this
warp, a focus error could still be generated.
[0101] As shown in FIG. 12, since a slim disc has a small substrate
thickness, its outer edge tends to bend easily downward due to its
own weight. By taking advantage of such a property of a slim disc,
the decision processing steps shown in FIG. 9, which are detailed
processing steps of Step 205 shown in FIG. 5 in the preferred
embodiment described above, may be replaced with the ones shown in
FIG. 13. The decision method shown in FIG. 13 can be applied
particularly effectively to such a situation where the outer edge
of a slim disc bends downward due to its own weight as shown in
FIG. 12.
[0102] FIG. 13 is a flowchart showing the procedure of a process
for determining whether or not the disc shown in FIG. 12 will
produce a significant axial runout. It should be noted that the
series of processing steps shown in FIG. 13 are supposed to be
started when the disc is still in rest position and is not rotating
yet. Thus, if the disc is already rotating, the servo section 106
is instructed to stop the disc motor 102 before the processing step
701 starts to be performed.
[0103] First, in Step 701, the slim disc recognizing section 108
issues a command as in Steps 401 and 503 to the servo section 106,
thereby instructing the transport section 109 to move the optical
head 103 to a radial location of 50 mm on the optical disc 101.
[0104] Next, in Step 702, the slim disc recognizing section 108
issues a command to the servo section 106 to turn the disc motor
102 one-fifth way around (i.e., 72 degrees). In this processing
step 702, the disc motor 702 may also be turned to any arbitrary
degree as long as it can be determined whether or not the disc is
producing a significant axial runout. In any case, one turn of the
disc is preferably divided evenly by an odd number (which may be a
prime number other than two). This is because if one turn of the
disc were divided evenly by an even number and if the disc were
producing an axial runout symmetrically to the disc radius as shown
in FIG. 12, then sometimes the decision could not be made
properly.
[0105] Subsequently, in Step 703, the slim disc recognizing section
108 issues a command to the servo section 106 to move the objective
lens (not shown) of the optical head 103 up toward the disc and
measure the amount of focus drive current that flows when the disc
surface or some storage layer is detected using a focus error
signal.
[0106] Next, in Step 704, these two processing steps 702 and 703
are carried out a number of times until the measurement can be done
the entire way around the disc. In this example, the same two
processing steps are repeated five times.
[0107] Thereafter, if it has been determined in Step 704 how much
focus drive current has flowed while disc has made one turn, then
the results of measurement that have been obtained in Step 703 are
compared to each other in the next processing step 705, thereby
confirming the magnitude of the variation. In this case, if the
difference between the maximum and minimum amounts of focus drive
current measured is equal to or greater than a focus drive current
value corresponding to the magnitude of the axial runout of the
disc of 0.3 mm, then the variation is determined to be
significant.
[0108] Next, if it has been determined in Step 706 that the
variation is significant as a result of the comparison that has
been made in the previous processing step 705, the process advances
to Step 707 in which the disc loaded is determined to be a slim
disc. On the other hand, if the answer to the query of the
processing step 706 is NO, then the process advances to Step 708 in
which the disc loaded is determined to be a non-slim disc.
[0109] As described above, by using the optical disc drive and
optical disc type recognition method of the preferred embodiment
described above, it can be determined whether or not the optical
disc loaded in the optical disc drive is a slim disc, and a read
operation can be performed with good stability even on a slim disc
that could produce a significant axial runout.
[0110] Optionally, the processing step 203 shown in FIG. 5 may be
replaced by one of the following two alternative processing steps
without performing the processing steps 401 to 403 shown in FIG. 8.
One alternative processing step is determining, by reference to the
disc size included in the disc identification information obtained
in Step 501 shown in FIG. 9, whether disc loaded is a 12 cm disc or
not. The other alternative processing step is determining, by
reference to the 8 cm disc's maximum storage capacity also included
in that disc identification information, whether the storage
capacity of the disc loaded is greater than the maximum storage
capacity of an 8 cm disc.
[0111] In the preferred embodiments of the present invention
described above, the optical disc drive is supposed to always
recognize the type of the disc loaded by itself. However, this is
just an example of the present invention. Alternatively, by using
some input device (not shown in FIG. 4), the user can tell the
optical disc drive whether the disc loaded in the optical disc
drive is a slim disc or not. In that case, the processing steps 201
through 206 shown in FIG. 5 can be omitted altogether.
[0112] It should be noted that the preferred embodiments of the
present invention described above are applicable to not just a
so-called "slim disc" but also any other disc that has a thinner
substrate or a lighter overall weight than a normal optical disc.
As for a BD, for example, its storage layer is located at a depth
of 0.1 mm under the disc surface. That is why a slim disc with a
substrate thickness of approximately 0.1 mm could be made by
reducing the thickness of the cover layer, and the preferred
embodiments of the present invention are also applicable to such a
slim disc with a substrate thickness of approximately 0.1 mm.
[0113] Furthermore, the preferred embodiments of the present
invention described above are also applicable to a bonded slim
disc, which has a combined substrate thickness of approximately 0.7
mm and in which a BD with a substrate thickness of 0.1 mm and a DVD
with a substrate thickness of 0.6 mm have been bonded together.
Therefore, the substrate thickness of slim discs does not have to
be 0.6 mm or less. Rather, the preferred embodiments of the present
invention described above are applicable to any slim disc as long
as it can be distinguished from a normal 12 cm disc in Step 201
shown in FIG. 5 by its substrate thickness (which may be 1.0 mm,
for example).
[0114] By using the optical disc drive and optical disc type
recognition method of the present invention, it can be determined
whether the disc loaded in the optical disc drive is a slim disc or
not, and a read operation can be performed with stability even on a
slim disc that could produce a significant axial runout. Thus, the
present invention is applicable effectively to recorders, players,
PCs and various other devices that use an optical disc.
[0115] While the present invention has been described with respect
to preferred embodiments thereof, it will be apparent to those
skilled in the art that the disclosed invention may be modified in
numerous ways and may assume many embodiments other than those
specifically described above. Accordingly, it is intended by the
appended claims to cover all modifications of the invention that
fall within the true spirit and scope of the invention.
* * * * *